1. Field of the Invention
This invention relates to a liquid crystal display, and more particularly to a liquid crystal display and a driving method wherein an application sequence of a data is changed so as to improve a picture quality.
2. Description of the Related Art
Generally, a liquid crystal display (LCD) uses a pixel matrix arranged in each intersection between gate lines and data lines to thereby display a picture corresponding to video signals. Each pixel consists of a liquid crystal cell controlling a transmitted light quantity in accordance with a video signal, and a thin film transistor (TFT) for switching the video signal to be applied from the data line to the liquid crystal cell.
The LCD is provided with gate and data driving integrated circuits, hereinafter referred to as “D-IC's”, for driving the gate lines and the data lines. In this case, a demultiplexor (DEMUX) is connected between the data D-IC so as to simplify a circuit configuration of the LCD.
The DEMUX reduces the required number of data D-IC by connecting any one output line of the data D-IC to a plurality of data lines. For instance, when the number of data lines is n and the number of data lines connected to one DEMUX, the output line number k of data D-IC becomes ‘n/m’. In other words, the required number of the data D-IC is reduced to ‘1/m’. The DEMUX is formed on the same substrate as the pixels upon manufacturing of the LCD.
The data D-IC outputs a data m times for one horizontal period 1H. The data outputted from the data D-IC is applied, via the DEMUX, to the data lines. The DEMUX receives control signals corresponding to the number of data lines allowable to itself so as to sequentially connect a plurality of data lines to one output line of the data D-IC.
Hereinafter, a conventional LCD driving method will be described with reference to FIG. 1 and FIG. 2.
Referring to FIG. 1, there is shown a conventional LCD device including first to kth demultiplexors DEMUX1 to DEMUXk connected to n data lines DL1 to DLn between a data D-IC 12 and a liquid crystal display panel 10. The data D-IC includes k output lines corresponding to the first to kth demultiplexors DEMUX1 to DEMUXk. Each of the k demultiplexors DEMUX1 to DEMUXk is connected to four data lines DL1 to DLn. To this end, each of the demultiplexors DEMUX1 to DEMUXk includes four MOS transistors MN1 to MN4.
The four MOS transistors MN1 to MN4 receive first to fourth control signals CS1 to CS4 from the exterior thereof. The first to fourth control signals CS1 to CS4 are sequentially enabled every horizontal synchronous interval as shown in FIG. 2.
The conventional LCD device further includes a gate D-IC 14 for driving m gate lines GL1 to GLm on the liquid crystal display panel 10. The gate D-IC 14 sequentially applies a gate scanning signal GSS to m gate lines GL1 to GLm for one frame.
The gate scanning signal GSS maintains a high state for one horizontal synchronous interval at a certain gate line GL as shown in FIG. 2. When the gate line GL maintains a high state, the data D-IC 12 sequentially applies four data to each of the demultiplexors DEMUX1 to DEMUXK. At this time, each of the demultiplexors DEMUX1 to DEMUXk responds to the first to fourth control signals CS1 to CS4 supplies four data inputted from the output line of the data D-IC 12 to four data lines.
More specifically, the first demultiplexor DEMUX1 receives four data R1, G1, B1 and R2 from the data D-IC 12 as shown in FIG. 2 and sequentially delivers them to the first and fourth data lines DL1 to DL4. Similarly, the second demultiplexor DEMUX2 receives four data G2, B2, R3 and G3 from the data D-IC 12 and sequentially delivers the same to the fifth to eighth data lines DL5 to DL8.
Such a conventional LCD driving method causes a phenomenon in which a data is distorted due to a coupling capacitor Cs between the data lines. More specifically, as shown in FIG. 3, the fifth data line DL5 receives a green data signal G2 from the first MOS transistor MN1 of the second demultiplexor DEMUX2 in a time interval when the first control signal CS1 has a high state. On the other hand, the fifth data line DL5 becomes a floating state when the first control signal CS1 has a low state. Then, the sixth data line DL6 receives a blue data signal B2 from the second MOS transistor MN2 of the second demultiplexor DEMUX2 in a time interval when the second control signal CS2 has a high state. At this time, a green data signal G2 charged in the fifth data line DL5 is changed due to the coupling capacitor Cc between the fifth and sixth data lines DL5 and DL6.
After the blue data signal B2 was charged in the second data line DL6, the seventh data line DL7 receives a red data signal R3 from the third MOS transistor MN3 of the second demultiplexor DEMUX2 in a time interval when the third control signal CS3 has a high state. At this time, the blue data signal B2 charged in the sixth data line DL6 is changed due to the coupling capacitor Cc between the sixth and seventh data lines DL6 and DL7.
After a red data signal R3 was charged in the seventh data line DL7, the eighth data line DL8 receives the green data signal G3 from the fourth MOS transistor MN4 of the second demultiplexor DEMUX2 in a time interval when the fourth control signal CS4 has a high state. At this time, a red data signal R3 charged in the seventh data line DL7 is changed due to the coupling capacitor Cc between the seventh and eighth data lines DL7 and DL8.
Further, the green data signal G2 charged in a pixel on the fifth data line DL5 is changed when the red data signal R2 is applied to the fourth data line D4. In other words, a data signal received from the first MOS transistor MNI is changed twice by the coupling capacitor while data signals received from the second and third MOS transistors MN2 and MN3 are changed once by the coupling capacitor. On the other hand, a data signal received from the fourth MOS transistor MN4 is not changed. As a result, a conversion frequency of the data signal is differentiated, so that a stripe-shaped distortion is generated at a picture displayed on the liquid crystal display panel 10.
In the conventional LCD driving method, a different leakage current is generated depending on an application sequence of data signals applied to the data lines DL1 to DLn. Such a different leakage current from the data lines DL1 to DLn is caused by a fact that a holding interval is different in accordance with an application sequence of the data signals. In other words, as shown in FIG. 4, a data having the same voltage value is sampled in a state changed into a different absolute voltage value from each pixel. More specifically, the first data line DL1 receives the first red data signal R1 from the first MOS transistor MN1 of the first demultiplexor DEMUX1 in a time interval when the first control signal CS1 has a high state. The first data line DL1 maintains a voltage charged until the falling edge of the gate scanning signal GSS. In other words, a voltage charged in the first data line DL1 is leaked for a long time from the falling edge of the first control signal CS1 until the falling edge of the gate scanning signal GSS. As a result, the first data line DL1 applies a voltage signal lower than the initially received red data signal R1 to the pixel. In other words, a voltage applied to the first data line DL1 is leaked by a voltage ΔV1.
The fourth data line DL4 receives the second red data signal R2 from the fourth MOS transistor MN4 of the first demultiplexor DEMUX1 in a time interval when the fourth control signal CS4 has a high state. The fourth data line DL4 maintains the charged voltage until the falling edge of the gate scanning signal GSS. The voltage charged in the fourth data line DL4 is leaked for a short time from the falling edge of the fourth control signal CS4 until the falling edge of the gate scanning signal GSS. As a result, a voltage applied to the fourth data line DL4 is leaked by a voltage ΔV2. Accordingly, the voltage applied to the fourth data line DL4 becomes higher than the voltage applied to the first data line DL1. For this reason, a picture displayed on the liquid crystal display panel 10 is more distorted to thereby deteriorate a picture quality.
As a result, in the conventional LCD driving method, the same data is supplied to each pixel at a different voltage level to thereby distort a picture displayed on the liquid crystal display panel. Also, since a color data supplied to each data line is changed by the coupling capacitor, a picture distortion phenomenon becomes serious.